1. Field of the Invention
This invention relates to switched reluctance motors, and more particularly to a bearingless switched reluctance motor.
2. Prior Art
Switched reluctance motors are typically constructed of a stator having an even number of poles, usually four or more, and a rotor having an even number of poles, also usually two or more. The poles on the rotor are typically oriented in a protruding manner crosswisely around the rotating shaft in an outward manner. The poles on the stator typically protrude inwardly with a concentrated winding thereabout in the form of a coil. The coils, which are wound on each of the pairs of opposing stator pole portions, are connected in series with each other whereby a magnetic flux is generated between each pair of opposing stator pole portions when current is supplied to the coils which are wound thereon.
In switched reluctance motors, the protruding poles of the stator attract the protruding poles on the outer peripheral surface of the rotor to generate torque and as a result, the rotor rotates. As a pole of the rotor approaches a pole of the stator, the supply current to the poles is changed, typically by means of switching elements in response to the rotational position of the rotor whereby rotatory torque is produced.
It is recognized that switched reluctance motors have advantages over reluctance, induction and permanent magnet motors due to their reliability, durability, low cost and possible operation in adverse environments including high temperatures, intense temperature variations or high rotational speeds. However, due to rotor eccentricity of rotors due to mechanical flaws during machining, conventional switched reluctance rotors suffer from vibration caused by large magnetic attraction forces on the rotor in the radial direction. Furthermore, traditional bearings are subject to wear and require lubrication.
Several patents have been obtained for improvements to switched reluctance motors including at least U.S. Pat. Nos. 5,909,071, 5,969,454, 5,880,549, 5,917,263, and 5,945,761. Few except the  greater than 549 Patent, if any, are directed to bearingless switched reluctance motors. Nevertheless at least these efforts to reduce the effects of vibration and noise in a switched reluctance motor have been made.
Bearingless switched reluctance machines, which are believed to have been achieved only in development laboratories so far, employ magnetic bearings instead of traditional bearings and are thus referred to as bearingless since there is no mechanical bearing between the rotor and the stator during operation. Of course, a mechanical bearing is usually provided should the magnetic bearing fail. By magnetically suspending the rotor relative to the stator, further efforts to suppress vibration may be employed.
U.S. Pat. No. 5,880,549 discusses a prior art switched reluctance motor construction. The rotor rotates relative to the stator while being levitated by magnetic forces. In addition to the  greater than 549 Patent, a number of papers have been authored by Akira Chiba, Masahiko Hanazawa, Ken Shimada, Tadashi Fukao, and Azizur Rahinan regarding bearingless switched reluctance machines. These individuals have studied the effects of magnetic saturation on a traditional bearingless switched reluctance motor, the mathematical formulations of forces affecting a traditional bearingless switched reluctance motor, and the addition of a feed forward compensator to adjust for the locus of magnetic centers. The studies of these individuals appear to center primarily around the use of a main four pole winding to rotate the rotor while utilizing a two pole winding to apply radial force to the winding with all of the stator poles having both windings thereon.
Accordingly, a need exists for an improved bearingless switched reluctance motor.
Consequently, it is a primary object of the present invention to provide a bearingless switched reluctance machine having higher load carrying capacity, higher stiffness and/or greater vibration suppression capacity.
It is a further object of the present invention to provide a rotor for use with a switched reluctance motor having higher load carrying capacity, higher stiffness and/or greater vibration suppression capacity.
Another object of the present invention is to utilize a single set of windings of a switched reluctance motor wherein a plurality of the poles are dedicated to levitation of the rotor while a separate plurality of poles are dedicated to rotating the rotor.
Accordingly, the present invention provides a bearingless switched reluctance motor having a stator with a plurality of pairs of poles and a hybrid rotor having a plurality of pole pairs in a laminated bundle on a first portion, and a stack of circular laminations forming a circular disc on a second portion. In the illustrated embodiment, an eight pole stator is utilized with a rotor having a first portion with six poles. Of course, other strator/rotor combinations could be utilized as well. A second portion is a disc member. Levitation may be produced and vibration may be suppressed by utilizing feed back and feed forward commands in the control software. The stator has four poles which are exclusively utilized to levitate or maintain the horizontal alignment of the rotor within the stator. The disc portions of the rotor is affected by the levitation poles of the stator. The other four poles are utilized in an opposing pair fashion to apply torque to rotate the rotor about the stator.